(SOLVED) UV Unwrapping does not work properly
As you can see if I select these faces and hide, I can see some &quot;floating&quot; edge loops here, they are creating these artifacts we see. You could delete them manually but if you select all and merge the vertices (AltM) you will probably get rid of them:

As for the unwrap, the method you need to use depends on what you want to do, if you don't plan to use an Image Texture you don't even need to unwrap actually. If you want to paint on your object in the 3D view, you can simply unwrap with the Smart UV Project option. If you plan to use an already made image and you need to make the UV match, mark some seams on you topology then unwrap with the Unwrap option.